1. Field of the Invention
The present invention relates to a technology of visualizing a sound field.
2. Description of the Related Art
Up to now, there have been proposed various technologies for visualizing a sound field (for example, refer to Non-patent documents 1 and 2). Non-patent document 1, Kohshi Nishida, Akira Maruyama, “A Photographical Sound Visualization Method by Using Light Emitting Diodes”, Transactions of the Japan Society of Mechanical Engineers, Series C, Vol. 51, No. 461 (1985) discloses that one microphone is moved vertically and laterally within a sound space, sound pressures at a plurality of places are sequentially measured, and a light emitter such as a light emitting diode (LED) emits a light with luminance corresponding to the sound pressure, thereby visualizing the sound field. On the other hand, Non-patent document 2, Keiichiro Mizuno, “Souon no kashika”, Souon Seigyo, Vol. 22, No. 1 (1999) pp. 20-23 discloses that a plurality of microphones are arranged within the sound space where a sound to be visualized is emitted to measure a sound pressure, a measurement result is tallied by a computer device, and a sound pressure distribution in the sound space is graphed and displayed on a display device.
The technology of visualizing a sound field performs a crucial function when grasping a noise distribution, for example, in rail cars or on airplanes and taking measures against noise. However, the purposes expected for the availability of the technology of visualizing the sound field are not limited to the use of analysis or reduction of the noise transmitted to the interior of the rail cars or the airplanes. In recent years, the availability of the sound field visualizing technique is expected for control of more soothing heard sound. For example, with the popularization of home audio devices with high performance which are represented by home theater, there is an increased need to use the sound field visualizing technology for the purpose of laying out the audio devices or adjusting the gains. The sound visualizing technology is expected to satisfy such a need. This is because if the sound pressure distribution of sound emitted into a sound space such as a living room, or a transition thereof (that is, a propagation state of sound wave) can be visualized, the layout position and the gain of the audio device can be appropriately adjusted so as to obtain a desired propagation state while visually confirming the propagation state, and it is expected that even end users having no specialized knowledge about audio can readily optimize the layout position of the audio device. Also, the sound field visualizing technology is expected to be applied to an intended purpose for reducing sound interferences called “flutter echo” or “booming” in the sound space such as a conference room or an instrument training room. Further, the sound field visualizing technology is also expected to be effective as a way for presenting a product test of a sounding body such as an instrument or a speaker (for example, a test of whether the instrument plays the sound as planned, or not), the design assistance, or the acoustic performance of products to the end user.
However, in the technology disclosed in Non-patent document 1 mentioned above, because one microphone is moved within the sound space to sequentially measure the sound pressure, the sound pressures at the plurality of places cannot be visualized at the same time (that is, the sound pressure distribution within the sound space cannot be visualized). On the other hand, in the technology disclosed in Non-patent document 2 mentioned above, although an instantaneous propagation state of sound in the sound space can be visualized, a computer device that tallies and graphs the sound pressures measured by the respective microphones is required, resulting in a large-scale system. For that reason, there arises such a problem that this technology cannot be readily used at home. Also, as in the technology disclosed in Non-patent document 2 mentioned above, the technology by which the sound field is visualized by the aid of the plurality of microphones (or a microphone array configured by the plurality of microphones) allows, in addition to a problem that the entire system is complicated, a problem that an influence of the installation of the microphones on the sound field (an influence of a main body of the microphone array, or an influence of a wiring between the microphone array and a signal processing device) is large. The technology also allows a problem that there is a need to acquire positional information representative of the layout positions of the respective microphones through another method, a problem that the expansion of the number of channels which has been decided once is difficult, and a problem that because there is a need to display the results collected by the microphones on another display device, the simultaneity and real time property of the positional information are lost so that the sound field cannot be instinctually visualized.